Changeset 6744793 in rtems-docs


Ignore:
Timestamp:
11/21/23 14:54:36 (3 months ago)
Author:
Christian Mauderer <christian.mauderer@…>
Branches:
master
Children:
ef49c46
Parents:
500ac0d
git-author:
Christian Mauderer <christian.mauderer@…> (11/21/23 14:54:36)
git-committer:
Christian Mauderer <christian.mauderer@…> (11/28/23 12:38:25)
Message:

bsps/imxrt: Document GPIO CS pins for LPSPI

File:
1 edited

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  • user/bsps/arm/imxrt.rst

    r500ac0d r6744793  
    199199pins on the Arduino connector.
    200200
     201By default, the native chip selects are used. If you want to use GPIOs as chip
     202select instead, you can use the `cs-gpios` and `num-cs` attributes just like on
     203a Linux SPI controller. A maximum of `IMXRT_LPSPI_MAX_CS` pins can be used.
     204
     205The hardware doesn't support selecting no native chip select during a transfer.
     206Therefore one native chip select has to be reserved as a dummy if you want to be
     207able to use GPIOs. The pin function for this chip select must not be configured
     208on any pin. Dummy will be the first of the first four chip selects that is not a
     209native one. Example configuration::
     210
     211  &lpspi4 {
     212    status = "okay";
     213    pinctrl-0 = <&my_pinctrl_lpspi4>;
     214    cs-gpios = <0>, <0>, <&gpio1 1 0>, <0>, <&gpio11 5 1>;
     215    num-cs = <5>;
     216  }
     217
     218In this case, CS2 will be the dummy chip select and no pin must be configured
     219with that function. CS0, CS1 and CS3 are just native chip selects and should be
     220used via pin functions. GPIO1.1 is used as a high active CS and GPIO11.5 a low
     221active one.
     222
    201223Limitations:
    202224
    203225* Only a basic SPI driver is implemented. This is mostly a driver limitation and
    204226  not a hardware one.
     227* GPIO CS pins on i.MXRT10xx are not tested. The chip has a lot of errate so
     228  they might not work.
     229* Switching from one mode (CPOL/CPHA) to another one can lead to single wrong
     230  edges on the CLK line if GPIO CS pins are involved. Make sure to stuff a dummy
     231  transfer with `SPI_NO_CS` set if you use multiple modes together with a GPIO
     232  CS.
    205233
    206234Network Interface Driver
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